1. Field of the Invention
The present invention relates primarily to the papermaking arts. Specifically, the present invention relates to seamable fabrics for use on papermaking machines, in addition to other industrial applications. More specifically, the present invention relates to seamable fabrics used as industrial process fabrics in the production of, among other things, wet laid products such as paper, paper board, and sanitary tissue and towel products; in the production of wet laid and dry laid pulp; in processes related to papermaking such as those using sludge filters, and chemiwashers; in the production of tissue and towel products made by through-air drying processes; and in the production of non-wovens produced by hydroentangling (wet process), melt blowing, spunbonding, and air laid needle punching. Such industrial process fabrics include but are not limited to non-woven felts; embossing, conveying, and support fabrics used in processes for producing non-wovens; filtration fabrics and filtration cloths. The term “industrial process fabrics” also includes but is not limited to all other paper machine fabrics (forming, pressing and dryer fabrics) for transporting the pulp slurry through all stages of the papermaking process. In particular, the present invention is related to fabrics of the variety that may be used to mold cellulosic fibrous web into a three-dimensional structure.
2. Description of the Prior Art
During the papermaking process, a cellulosic fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, onto a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric, leaving the cellulosic fibrous web on the surface of the forming fabric.
The newly formed cellulosic fibrous web proceeds from the forming section to a press section, which includes a series of press nips. The cellulosic fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two such press fabrics. In the press nips, the cellulosic fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere the cellulosic fibers in the web to one another to turn the cellulosic fibrous web into a paper sheet. The water is accepted by the press fabric or fabrics and, ideally, does not return to the paper sheet.
The paper sheet finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The newly formed paper sheet is directed in a serpentine path sequentially around each in the series of drums by a dryer fabric, which holds the paper sheet closely against the surfaces of the drums. The heated drums reduce the water content of the paper sheet to a desirable level through evaporation.
It should be appreciated that the forming, press and dryer fabrics all take the form of endless loops on the paper machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process, which proceeds at considerable speeds. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section.
Contemporary fabrics are produced in a wide variety of styles designed to meet the requirements of the paper machines on which they are installed for the paper grades being manufactured. Generally, they comprise a woven base fabric which, depending upon the application may include needled batt of fine, non-woven fibrous material. The base fabrics may be woven from monofilament, plied monofilament, multifilament or plied multifilament yarns, and may be single-layered, multi-layered or laminated. The yarns are typically extruded from any one of the synthetic polymeric resins, such as polyamide and polyester resins, used for this purpose by those of ordinary skill in the paper machine clothing arts.
The woven base fabrics themselves take many different forms. For example, they may be woven endless, or flat woven and subsequently rendered into endless form with a woven seam. Alternatively, they may be produced by a process commonly known as modified endless weaving, wherein the widthwise ends of the base fabric are provided with seaming loops using the machine-direction (MD) yarns thereof. In this process, the MD yarns weave continuously back-and-forth between the widthwise ends of the fabric, at each end turning back and forming a seaming loop. A base fabric produced in this fashion is placed into endless form during installation on a papermachine, and for this reason is referred to as an on-machine-seamable (OMS®) fabric. To place such a fabric into endless form, the two widthwise ends are brought together, the seaming loops at the two ends are interdigitated with one another, and a seaming pin or pintle is directed through the passage formed by the interdigitated seaming loops.
Further, the woven base fabrics may be laminated by placing one base fabric within the endless loop formed by another, and by needling a staple fiber batt through both base fabrics or by using resin(s) to join them to one another. One or both woven base fabrics may be of the on-machine-seamable type.
U.S. Pat. No. 5,769,131 shows an on-machine-seamable papermaker's fabric that includes flat machine-direction yarns which define the upper and lower surfaces of the fabric. The fabric has two layers of cross-machine-direction yarns, each of which is interwoven with the flat machine direction yarns. Other machine-direction yarns, of round cross section, weave with the cross-machine-direction yarns in the two layers to bind the two layers together. The fabric is seamed into endless form during installation on a paper machine. At one of the two ends of the fabric, seaming loops are formed by the flat machine-direction yarns. The seaming loops are interdigitated with one another when the two ends of the fabric are brought together during installation on the paper machine, defining a passage through which a seaming pin or pintle may be directed to join the two ends to one another.
In any event, the woven base fabrics are in the form of endless loops, or are seamable into such forms, having a specific length, measured longitudinally therearound, and a specific width, measured transversely thereacross. Because paper machine configurations vary widely, paper machine clothing manufacturers are required to produce fabrics, and other paper machine clothing, to the dimensions required to fit particular positions in the paper machines of their customers. Needless to say, this requirement makes it difficult to streamline the manufacturing process, as each fabric must typically be made to order.
In response to this need to produce fabrics in a variety of lengths and widths more quickly and efficiently, press fabrics have been produced in recent years using a spiral technique disclosed in commonly assigned U.S. Pat. No. 5,360,656 to Rexfelt et al., the disclosure of which is incorporated herein by reference.
U.S. Pat. No. 5,360,656 shows a press fabric comprising a base fabric having one or more layers of staple fiber material needled thereinto. The base fabric comprises at least one layer composed of a spirally wound strip of woven fabric having a width which is smaller than the width of the base fabric. The base fabric is endless in the longitudinal, or machine, direction. Lengthwise threads of the spirally wound strip make an angle with the longitudinal direction of the press fabric. The strip of woven fabric may be flat-woven on a loom which is narrower than those typically used in the production of paper machine clothing.
The base fabric comprises a plurality of spirally wound and joined turns of the relatively narrow woven fabric strip. The fabric strip is woven from lengthwise (warp) and crosswise (filling) yarns. Adjacent turns of the spirally wound fabric strip may be abutted against one another, and the helically continuous seam so produced may be closed by sewing, stitching, melting or welding. Alternatively, adjacent longitudinal end portions of adjoining spiral turns may be arranged overlappingly, so long as the ends have a reduced thickness, so as not to give rise to an increased thickness in the area of the overlap. Further, the spacing between lengthwise yarns may be increased at the ends of the strip, so that, when adjoining spiral turns are arranged overlappingly, there may be an unchanged spacing between lengthwise threads in the area of the overlap.
In the case of dryer fabrics, in particular, such fabrics were produced by flat weaving and then joined together. Dryer fabrics that are used today are too long and require a seam for installation, since dryer section frames are solid without contilever components and thus prevent the use of endless woven fabrics. Accordingly, the fabrics must be installed with a seam, since they cannot be put on endless.
It should be noted that contemporary fabrics also include fabrics with non-woven bases. An example of a non-woven fabric is shown in U.S. Pat. No. 4,427,743, which discloses a wet press felt for use on papermaking machines. The wet press felt includes a conventional felt fabric and a multiple of non-woven layers of synthetic textile fibers needled to the felt. Interposed between the layers of synthetic textile fiber are mesh fabrics which support the individual non-woven layers and retard compaction of the overall construction. Such non-woven fabrics may be provided with seams like those of the woven fabrics in order to realize an “endless” non-woven fabric.
In addition to the aforenoted modified endless weaving which provides a seamable fabric, there exists other types of seams heretofore utilized, particularly in the case of dryer fabrics. For example, some flat woven dryer fabrics had clipper hook seams as are used in corrugator belts today. However, clipper hooks tend to corrode. More importantly, clipper hooks wear, do not flex well (they tend to bump around fabric support rolls), and the seam tends to mark the paper sheet.
Some fabrics are seamed on a diagonal in a manner as set forth in U.S. Pat. No. 5,217,415 which has been found satisfactory for certain applications.
Seams can also be sewn on which involves a webbing sewn onto both cross-machine direction (“CD”) ends of the dryer fabric. The webbing contains loops which are meshed together to form the seam. The webbing, since it is out of plane and thicker than the fabric body, also tends to bump around fabric support rolls, marks the sheet, and has zero permeability, which further exacerbates the sheet marking problem. Since it is sewn on, the stitching is between the web and the fabric body. Once the stitching fails, the web will pull off, resulting in a “seam failure”.
Some fabrics have the aforesaid pin seams, however, with or without a spiral insert. These dominate the market today. All these seams require MD yarns to be woven back into the structure body by hand or machine assisted. CD yarns must be raveled out. Yarn materials, counts and sizes, weaves dictate the seam properties and the seam properties (uniformity, strength) dictate yarn counts within a certain weave. These seams are expensive to make, since they are labor intensive. The strength and seam durability are dictated by material properties too, especially loop strength. “Brittle” materials which have poor loop strength but may have other good properties are not dryer fabric candidates because of this. To compensate for low seam loop strength one may have to compromise on the fabric structure itself. An example of a seam having a spiral insert can be found in U.S. Pat. No. 5,915,422.
Early metal forming fabrics which were flat woven and shipped open ended, were installed on the machine with the metal wire ends joined together by brazing or fusing the yarns by heat. This “butt seam” had some slight end overlap and the seam only lasted for a short period of time. There was no sewing, stitching, or adding in a synthetic spiral.
Another example of a butt seam can be found in the aforementioned U.S. Pat. No. 5,360,656. This seam is between adjacent strips of fabric and includes stitching. The seams, however, are not load bearing and are merely there to hold the strips together so that the “base” structures formed by these joined together strips can be handled through the manufacturing process.
Obviously, there are other ways to provide seamable fabrics for use in papermaking and other industrial applications, with the foregoing being set forth merely as examples. However, as with anything, there is always a desire to improve on or provide an alternative to what has been done previously. Seamable fabrics are no exception. In this regard, heretofore providing a seam on a fabric has been relatively time consuming and labor intensive. If these are aspects that can be improved upon, this would obviously be a desirable result.